1. Field of the Invention
The present invention relates to a method for distinguishing between real obstacles and apparent obstacles in a driver assistance system for motor vehicles equipped with a position finding system for determining one's own location, as well as a radar sensor for measuring distances and relative velocities of radar targets.
2. Description of the Related Art
Electronic driver assistance systems are known that assist the driver in controlling the vehicle, in particular on the basis of information provided by the radar sensor, for example, by issuing a warning or automatically triggering an intervention in the form of an emergency braking in response to an acute accident risk.
To ensure that such driver assistance systems improve road safety, it is important that incorrect interventions, such as false warnings or brake interventions that are unnecessary—and thus unexpected for any following traffic—be avoided to the greatest extent possible. This presupposes that the system be able to use the available information to reliably distinguish between real obstacles that require a warning or an intervention and apparent obstacles that the radar sensor does, in fact, detect, but are not real obstacles. Examples of such apparent obstacles are, for instance, metal manhole or sewer covers, cow grids and the like, which, however, because of the high reflectivity thereof to radar waves from the radar sensor, are not actual obstacles since the vehicle can easily drive over them. Due to the limited angular resolving power thereof, the customary radar sensors are not able to estimate the dimensions, in particular the height, and the exact position of the located object reliably enough to make these objects distinguishable from real obstacles, such as stationary vehicles and the like.
By comparing the relative velocity of a located object to the velocity of the host vehicle, the driver assistance system is able to distinguish between objects that are absolutely stationary (relative to the road surface) and those that are moving. In the case of moving objects on the road surface, whose relative velocity is negative (thus, which are approaching), it can generally be assumed that they are real obstacles. On the other hand, in the case of stationary radar targets, it is difficult to make the distinction. Evaluation algorithms have, in fact, been developed that make it possible to additionally check the plausibility of the obstacles. However, these algorithms are not reliable in all situations.
It is also known to consult data from additional sensors, for instance, the data from a video camera and a corresponding image processing system for plausibility checking or verification of obstacles. However, these more expensive evaluation methods require considerable computing power, respectively computing time.